Stormont House (also called Speaker's House) is the headquarters of the Northern Ireland Office, situated in the Stormont Estate in Belfast, Northern Ireland. It was designed by Ralph Knott, although Sir Edwin Lutyens has been credited with some involvement. It served as the official residence of the Speaker of the House of Commons of Northern Ireland between 1921 and 1972. For part of the time it was actually lived in by a number of Prime Ministers of Northern Ireland in preference to their own official residence, Stormont Castle, which was used primarily as offices.